This application claims the priority of German patent document 100 01 717.7, filed Jan. 18, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a fuel cell system having one or more fuel cell units inserted into a fuel cell box. Allocated to the fuel cell units are one or more of are a cathode gas delivery line, a cold-start gas delivery line, a cathode off-gas return line and an anode off-gas return line. Fuel cell systems of this type are used, for example, as an energy supply for electric vehicles.
Delivery or discharge of gas streams by a gas stream propelling means are provided in conventional fuel cell systems; usually by fans, blowers, ventilators and compressors. In other fields, however, it is known to use Coanda flow amplifiers. By supplying a driving flow medium at relatively high pressure and in a relatively small amount, such flow amplifiers can drive a flow of a second flow medium at relatively low pressure but high volume flow rate by exploiting the Coanda effect. To this end the Coanda flow amplifier designed in the form of a nozzle gap has a suitable internal or alternatively external flow wall surface for a wall-hugging flow of the drive medium supplied at elevated pressure.
Coanda flow amplifiers of this type are commercially available, for example, from EXAIR Corp. as air flow amplifiers and also from other suppliers under the description of xe2x80x9cair amplifiersxe2x80x9d. Their delivered air flow can be used for cooling, drying, cleaning or ventilation, or their aspirated air flow can be used for the extraction of off-gases, vapors, smoke and dusts.
International patent document WO 98/32964 discloses an internal combustion engine with exhaust gas recirculation, in which the exhaust gas return line has a Coanda flow amplifier connected, via its high-pressure connection, to the compressed-air source of a compressed-air braking system of a motor vehicle. A special design of a Coanda flow amplifier to generate a helical fluid flow is disclosed in European patent document EP 0 456 931 B1.
One object of the present invention is to provide a fuel cell system of the type first mentioned above, which operates with relatively few components requiring electrical actuation.
These and other objects and advantages are achieved by the fuel cell system according to the invention, which is equipped with one or more Coanda flow amplifiers.
In one embodiment of the invention, a Coanda flow amplifier is provided in a purge gas line via which purge air can be introduced into a fuel cell box and discharged therefrom in order to ventilate said box.
In another embodiment of the invention, a Coanda flow amplifier is disposed in a delivery line to supply a cathode-side gas stream to the fuel cell and/or in a delivery line via which a cold-start gas is supplied to the at least one fuel cell unit. The cold-start gas feeds a cold-start component which brings the system to operating temperature as rapidly as possible in the event of a cold start.
In still another embodiment, a Coanda flow amplifier is provided in a cathode off-gas return line which recirculates at least part of the cathode off-gas to the cathode inlet side, thereby improving the water balance of the system.
In yet another embodiment, a Coanda flow amplifier is disposed in an anode off-gas return line and is connected, via a compressed-gas inlet, to a gas reservoir in which fuel (e.g., hydrogen) is stored under pressure.
In a refinement of the invention, the Coanda gas amplifier disposed in the cathode gas delivery line and/or cold-start gas delivery line has a high-pressure compressor connected to it on its upstream side. The compressor pressurizes the drive gas, which is used for gas amplification in the Coanda flow amplifier, to an adequate pressure.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.